Flexible sheet-like magnetic discs having a nominal standardized size of about 3.5-inches are widely used in a variety of data storage/retrieval systems. For example, cassettes which include flexible magnetic discs are used in conjunction with personal computers so as to load data and/or programs into the central processing unit of the computer, as well as to store data in an off-site location in a more convenient manner.
When placed into service in a magnetic recording/reproducing apparatus, the magnetic disc (which is accommodated for rotational movement within the interior of the cassette case) is caused to spin relative to a magnetic read/write head by means of a motor-driven spindle coacting with an aperture in the central hub of the magnetic disc. The spindle, moreover, serves to center the magnetic disc relative to the magnetic read/write head so that accurate placement and retrieval of data onto and from the disc will ensue.
The cassette case for flexible magnetic discs having a standardized size of about 3.5-inches (i.e., so-called "microdiscs") is relatively thin (i.e., on the order of about 0.14 inch (3.4 mm)). In this regard, it has been the industry practice for some time to physically join the cassette case halves (which are typically made of an ABS (acrylonitrile-butadiene-styrene) resin) using ultrasonic welding techniques. Although mateable male/female projections have been formed on the interior of conventional cassette case halves in order to provide "locators" they do not serve to physically couple the cassette halves one to the other. Instead, the cassette case halves are typically joined to one another by ultrasonic welding. (See in this regard, U.S. Pat. No. 4,517,617 to Tsuji et al, incorporated by reference herein).
Several problems, however, are associated with the ultrasonic welding of the cassette case halves. For example, ultrasonic welding of the cassette case halves requires vibration at ultrasonic frequencies to be imparted to the cassette case at localized regions so as to generate the necessary frictional abrasion to provide for localized temperature increases sufficient to at least partially melt the cassette case in the localized regions, so that upon resolidification, the cassette case halves are irreversibly joined to one another. The frictional abrasion necessary to achieve localized temperature increases, however, typically generates a sufficient amount of dust-like particles which remain contained within the cassette case. As one means of solving this problem, conventional microdisc cassettes have also included non-woven fabric protector and an associated lifter (which serves to bias the fabric protector into physical engagement with the flexible magnetic disc) so as to prevent the dust generated from the ultrasonic welding operation from disrupting the proper reading/writing of information from/onto the flexible magnetic disc.
During fabrication of conventional microdisc cassettes, a final quality check is performed on the magnetic media prior to shipment of the microdisc to the purchaser. Oftentimes, however, the flexible magnetic media does not satisfy quality standards (e.g., due to defects that may have occurred during handling as part of the fabrication process) and therefore must be segregated from the acceptable disc products. Because the cassette case halves have been irreversibly joined to one another via ultrasonic welding, the defective flexible magnetic disc cannot simply be replaced with a disc of acceptable quality. As a result, the entire assembled microdisc cassette must be scrapped--a costly necessity due to the labor investment that is involved in the fabrication process.
It would be especially desirable if means were provided to allow the cassette case halves of microdiscs to be joined one to another without ultrasonic welding. Such an improvement could possibly eliminate the need for fabric protectors which are provided with conventional microdisc cassettes, and thereby save the labor/handling costs associated with the same. In addition, the cassette case could be fabricated more easily with the cassette case halves being readily separable to allow defective magnetic media to be replaces. As a result, the entire microdisc cassette would not need to be scrapped. It is towards achieving such improvements to microdisc cassettes that the present invention is directed.
According to the present invention, novel microdisc (i.e., standardized 3.5-inch magnetic "floppy" discs) cassette cases formed of a molded thermoplastic material are provided whereby the opposing halves are joined to one another in face-to-face relationship without necessarily employing ultrasonic welding techniques. More specifically, the present invention includes joining the opposing cassette case halves one to another by means of frictionally interengaged male and female detent members which are formed as one-piece structures with respective ones of the cassette case halves. Preferably, the frictional interengagement between the male and female detent members provide the sole means by which the cassette case halves are joined.
The male and female detent members each have a peripheral edge which defines a generally annular interengagement region. That is, the peripheral edges of the male and female detent members will each frictionally engage one another within the generally annular region circumscribed by each. This annular region of frictional interengagement between the male and female detent members is beneficial as it maximizes the amount of interference fit therebetween, while minimizing the detent members' depth dimension (i.e., as measured perpendicular to the plane of the cassette case halves). In this regard, the width dimension of the generally annular interengagement region (i.e., as measured in a plane parallel to the plane of the cassette case halves) is at least about two times, and most preferably at least about three times, the interengagement region's depth dimension.
According to some embodiments of this invention, the male detent members are in the form of a projecting nib having an enlarged cylindrical head portion. The female detent member, on the other hand, will be in the form of a conforming annular upright wall which defines a space that is sized and configured to accept the enlarged cylindrical head of the male nib therewithin. The annular upright wall will moreover preferably define an entranceway of reduced dimension so as to enhance the interference fit between the enlarged head of the male nib and the space defined by the upright annular wall.
Another embodiment of this invention includes a number of discrete walls arranged so as to circumscribe generally the annular interengagement region. In its preferred form, the discrete walls of the male detents will each project outwardly from their associated cassette case half in converging relationship to one another. The discrete walls of the female detents, however, will each project outwardly from their respective cassette case half but in a diverging relationship to one another. The walls of the male detents will thus be in interference fit on an exterior lateral side of the walls of the female detents within the annular interengagement region defined thereby.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.